The self has long been an important concept in theoretical discussions of mental health and psychological well-being. However, traditional formulations are limited in that they tend to view the self as an isolated psychological unit. Conceptualizing the self in symbolic interactionist terms as a structure of role-identities corrects for this deficiency by explicitly incorporating the effects of social interaction, social support, and the larger social structure. Moreover, recent empirical work show that this symbolic interactionist conceptualization of the self has clear implications for mental health. The immediate goal of this proposal is to advance our understanding of the self as a structure of role-identities. Data representing questionnaire responses in a two-wave panel study of a sample of blood donors has already been collected. Three sets of analyses focusing on the blood donor role-identity are planned. First, the issue of self-concept stability will be examined for four distinct types of change. Second, a number of latent variable structural equation models will be estimated to explain self-concept change. And third, a novel approach to the measurement of self-definition will be developed and tested. These three sets of analyses will move us beyong previous research in this area by: a) bringing together many relevant theoretical variables in a single study, b) analyzing data in a longitudinal design, and c) employing sound measurement in models designed to control for measurement error. Thus, this research will give us a better understanding of the self as a structure of role-identities and should therefore have the more distant benefit of extending our understanding of the relationship between the self-concept and mental health.